The present invention generally relates to environmental control systems, such as heating, ventilation, and air conditioning (HVAC) systems, which can be used to control the temperature and humidity of common spaces, e.g., as can exist in data centers containing server computers. More, specifically the present invention can relate to efficiently operating the modules in an optimized manner (e.g. energy and/or monetary cost), while providing desirable environmental conditions.
Modern datacenters use HVAC systems to control indoor temperature, humidity, and other variables. It is common to have many HVAC units deployed throughout a data center. They are often floor-standing units, but may be wall-mounted, rack-mounted, or ceiling-mounted. The HVAC units also often provide cooled air either to a raised-floor plenum, to a network of air ducts, or to the open air of the data center. The data center itself, or a large section of a large data center, typically has an open-plan construction, i.e. no permanent partitions separating the air in one part of the data center from the air in another part. Thus, in many cases, these data centers have a common space that is temperature-controlled and humidity-controlled by multiple HVAC units.
HVAC units for data centers are typically operated with decentralized, stand-alone controls. It is common for each unit to operate in an attempt to control the temperature and humidity of the air entering the unit from the data center. For example, an HVAC unit may contain a sensor that determines the temperature and humidity of the air entering the unit. Based on the measurements of this sensor, the controls of that HVAC will alter operation of the unit in an attempt to change the temperature and humidity of the air entering the unit to align with the set points for that unit.
For reliability, most data centers are designed with an excess number of HVAC units. Since the open-plan construction allows free flow of air throughout the data center, the operation of one unit can be coupled to the operation of another unit. The excess units and the fact that they deliver air to substantially overlapping areas provides a redundancy, which ensures that if a single unit fails, the data center equipment (servers, routers, etc.) will still have adequate cooling.
As mentioned above, the standard operating procedure for the HVAC units is to control the return air temperature into each HVAC unit. Such operation is not aware of the temperature of the air entering the servers and other computing equipment in the data center. Since this information is not available to the HVAC unit controls or to the data center operators, the extra HVAC units are typically run at all times, to ensure that the servers are kept cool. However, such precautionary measures waste energy.
While it is possible to manually turn off redundant HVAC units to save energy, doing so poses a risk of overheating that equipment. Also, some data centers have variable loads, in which case it may be necessary to stop and start several units throughout the day. Furthermore, the complex and tightly coupled airflow patterns in a data center make it difficult for an operator to know which HVAC unit will be the most effective to restart should a need be identified.
Additionally, current methods ignore the cost (e.g., energy usage or maintenance) of HVAC units when determining how to control the units. Current methods can also be unstable if more complex algorithms are attempted.
Therefore, it is desirable to provide methods and systems that can account for costs of operating an HVAC system, and that are stable when accounting for redundant HVAC units.